Effects similar to some of those achieved by the invention can be produced on an electric guitar with multiple pick-ups (transducers which convert string vibrations to electric current). Each pick-up has a volume control. A selector switch determines which pick-up is connected to the output. If two pick-ups are set to different volumes, a tremolo effect can be achieved by sustaining a note or chord on the guitar and rapidly toggling the selector switch. Typically, one of the volumes is set to zero so the sound cuts in and out completely, resulting in a stuttering effect. The tremolo can be at a steady rate, a more complex rhythmic pattern, or sporadic. The switch can also be used to ‘turn on’ single notes or chords.
Disadvantages of the toggle switch method include:                It only works on those electric guitars where the volume controls are connected between the pick-ups and the selector switch. In most guitars, the volume controls come after the selector switch.        The typical pick-up selector is difficult to manipulate quickly. Fast tremolo effects can become tiring to the user and the timing of effects can be inaccurate.        An audible ‘click’ or ‘pop’ can be introduced by the instantaneous volume change. For this reason, the toggle switch method is used almost exclusively by guitarists who use heavily distorted guitar tones. The distortion (added to the signal by an effects unit such as a guitar foot pedal or by tube saturation in an amplifier) masks any clicking sound.        
In an attempt to emulate the toggle switch method, some guitarists wire a switch (commonly known as a ‘kill switch’) between the audio signal and the ground. Mounted on the face of the guitar, these spring-loaded switches short the signal, allowing a path for the live signal to leak to the ground. When pressed, they mute the output. When released, the spring returns the switch to the off position and the guitar signal is no longer muted.
Disadvantages of the kill switch method include:                A permanent alteration to the instrument is required.        The ‘clicking’ sound discussed earlier is, again, audible.        The switch contacts can arc as they are brought close together, introducing unwanted noise.        More unwanted noise can be introduced by ‘contact bounce’ (the springiness of the contacts cause them to bounce on and off each other several times before settling).        A positive physical movement by the user controls the silence, not the sound. This is counterintuitive and can be difficult to keep rhythmically accurate.        The switch is limited to shorting the entire signal.        
A Removable Inline Signal Interrupter for Electric Guitar proposed by Dennis Armstrong, (Brick, N.J., US) (United States Patent Application 20080178727) attempts to create a kill switch without the need for modification to the instrument.
Disadvantages of Dennis Armstrong's Signal Interrupter include:                Aside from avoiding permanent alteration to the instrument, all the shortcomings of the kill switch discussed earlier are inherited.        The audio signal travels through wiring (or some other conduit) and a switch, even when the device is not in use. This degrades the audio quality.        Within the switch, the audio signal disconnects from one contact before it connects with the other. This is equivalent to pulling the cord in and out of the guitar and introduces unwanted ‘buzz’ and ‘thud’ noises.        The signal is never shorted. Even when the volume control is at zero, the input to the amplifier is left open. Hum or noise accumulated between the volume control and the amplifier is still audible.        
The invention described herein and which is the subject of this application has numerous advantages over the existing state of the art. These advantages include the following:                It works with any standard electric instrument or electrified acoustic instrument.        The spring-operated push switch can be quickly and accurately manipulated with little effort.        All volume changes are smooth. It can even be used with an electric guitar with a clean tone and acoustic instruments without introducing undesirable ‘clicks’.        No alteration to the instrument is required.        It can be easily moved from one instrument to another.        The use of an opto-electronics to isolate the audio signal from the control switch reduces potential problems arising from arcing or contact bounce.        The choice between two modes—controlling the silence and controlling the sound—offers great flexibility to the user.        The signal is shorted and thus is genuinely silent when required.        The use of an opto-electronics to isolate the audio signal from almost all mechanical and electronic components leaves the audio signal pristine. The exception is a light sensitive (photosensitive) resistor which has little or no effect on the tonal quality of the output.        